The purpose of this invention is to deliver a stream of molten glass, at maintained temperature, to a remote location and particularly to combine two streams of molten glass in a location of limited size and accessibility.
Existing glass coating techniques involve the introduction of multiple glass streams in the forehearth or furnace section of the glass forming operation. This requires new equipment to be installed for the handling of main glass stream as well as the coating glasses.
Typical patents showing such construction, for example, are U.S. Pat. Nos. 1,828,217, 3,291,584, 3,554,726, 3,960,530, 4,023,953, 4,217,123, 4,299,609, 4,381,932 and 5,204,120.
Conventional forehearths for glass delivery are constructed of refractory brick. The glass is contained in a horizontal bath. Heat is maintained by radiant heating from combustion burners above the bath. Bath depth is limited to about 10" due to the practical limitations of infrared heat penetration. Alternately, electric current may be passed through the molten glass to maintain temperatures.
In either case, the glass is contained within the refractory ceramic brick. In a typical forehearth, the innermost refractories are very dense to resist glass attack. The outer layers are progressively less dense for their insulation properties. The overall wall thickness is typically from 10 to 18 inches. The overall width of the forehearth is several feet, therefore the placement of two forehearths in order to combine two glass streams is not possible.
The present invention provides for conveying glass from a remote location without the need for heavy refractories and radiant heating and in close proximity (4" to 12") to another glass stream.
The present invention is directed to a method and apparatus for delivering a glass stream comprising a first inner layer and a second outer layer, comprising a generally vertical orifice, delivering molten glass from a first source through said orifice, and delivering glass from a second source such that the glass from said second source provides an outer layer about the glass from the first source as it flows through said orifice.
Among the objectives of the present invention are to provide an improved method and apparatus for conveying the glass from the second source to provide the outer layer; wherein the glass is conveyed while efficiently maintaining uniformity of temperature of the glass; wherein a tube is heated by resistance heating; wherein the tube is constructed and arranged for efficient and uniform temperature distribution along the length of the tube; which is similar in function and smaller in design than a conventional forehearth; which minimizes changes in existing glass delivery equipment for the primary glass stream; which allows complete glass containment; and which provides for desired hydrostatic head pressure of the secondary glass stream.
In accordance with the invention, a resistance heated tube assembly is made of platinum or material having similar resistance heating properties and extends from a glass source for the outer layer to the orifice through which the glass flows from a glass source for the inner layer. The tube assembly includes a tube portion having an inlet end that communicates with the source for the outer layer and an outlet end. The tube portion has an axis positioned at any angle ranging between the horizontal and vertical but preferably has an axis which is more vertical than horizontal. Flanges are secured to the ends of said tube portion and the flanges are connected to an electric power supply. The cross sectional thickness of said flanges is preferably greater than the thickness of the tube portion. Each flange includes an annular groove adjacent its respective end of the tube portion into which the end of said tube portion extends. The flanges are welded to the tube portion. Flange heater modules surround each end of the tube portion.